The present invention relates to glazings.
Enclosures closed by transparent glazings receive strong solar loads, especially in summer. This is notably the case for the passenger compartment of a vehicle, and also for horticultural greenhouses and house walls exposed to the South or East-West. The temperature inside the enclosure increases and becomes too high for the objects or the plants which are placed therein or for persons who are in there or who are induced to penetrate therein.
It is known that this drawback is partly overcome by staining the glass glazing so that a fraction of the solar load is reflected, without however affecting the transparence and the passengers"" visibility to the outside of the vehicle. Windows with double glazing are also known wherein the internal space thereof is filled with gas having a low thermal conductivity at a relatively low pressure. It is thus possible to substantially reduce heat transfer by convection. U.S. Pat. No. 4,928,448 describes such a device. However, thermal isolation obtained in this way does not provide an obstacle to the solar load transferred through radiation.
Double glazing windows are also known. Depending on insolation, either an insulating liquid is introduced between the walls or the liquid is emptied from the inter-wall space which contains it. U.S. Pat. No. 5,787,652 describes such a vehicle window. The radiated heat is absorbed by the insulating liquid which transfers it to the inside of the vehicle by conduction and by convection.
The object of the present invention is to solve the posed problem by limiting the effects of radiated solar loads, notably in the case of a stopped vehicle when air-conditioning is no longer running. The present invention also aims at finding a remedy for the posed problem without affecting the glazing""s transparence.
The glazing according to the invention has variable absorptivity. It comprises two transparent, notably glass walls. Other transparent materials other than glass may also be contemplated, notably synthetic plastics. These two walls provide an inter-wall space. Depending on the individual case, the latter contains
either a first transparent fluid, notably a gas such as air, transferring solar energy in the transparence wavelength bands of said walls,
or a second fluid transparent in the visible portion of the electromagnetic spectrum, absorbing solar energy on a very wide portion of the electromagnetic spectrum, notably water in the liquid state or water in the liquid state with alcohol added.
In the first case, the glazing""s transparence in the visible portion of the electromagnetic spectrum is not affected and the glazing transfers the major portion of the solar load which it receives.
In the second case, the glazing absorbs the major portion of the solar energy which it receives, while remaining transparent in the visible portion of the electromagnetic spectrum. Indeed, water in the liquid state has the property of transparence, notably when it is in a thin layer under thicknesses from 1 to 2 millimeters. On the other hand, water in the liquid state has properties close to those of a black body absorbing solar radiations. Water in the liquid state as a thin layer does not provide an obstacle to transparence and furthermore, the small thickness of inter-wall space blocks convective motions. Hence, in this second case, the glazing is a radiation shield.
According to another essential characteristic feature of the invention, the glazing comprises a circuit for discharging energy located at its periphery. Preferably, the circuit for discharging energy located at the periphery of the glazing is a bead-shaped exchanger, with a heat pipe effect. Also advantageously, the second fluid absorbing solar energy is under its vapor pressure. It vaporizes and condenses in the free space within the bead. Heat energy absorbed by said second insulating fluid (in the sense of the present description, the expression xe2x80x9cinsulating fluidxe2x80x9d refers to an absorbing fluid or liquid) is thus dissipated at the periphery of the glazing towards the outside. The exchange surface is calculated in order to discharge heat towards the outside, by convection and conduction.
In the configuration of the second case, when the interwall space is filled with the insulating liquid, the glazing is thus well adapted for a stopped vehicle receiving a high solar load. Although the air conditioning is no longer running as the engine is stopped, the temperature inside the vehicle remains moderate. The passenger which now climbs into his vehicle no longer has to wait for the air-conditioning to be running again at its standard rating in order to feel the well-being of a moderate temperature.
Nevertheless, the driver may consider that the shield of water in the liquid state affects his/her visibility and may prefer to drive his vehicle while benefiting from maximum visibility, that obtained in the situation where the fluid filling the inter-wall space is air, or where the second fluid is under its vapor pressure. The effect of the solar load is then compensated by the air-conditioning which has been able to start after starting the engine.
Preferably, according to a complementary feature of the present invention, the glazing further includes means for filling or emptying the inter-wall space in order to fill said space with said second fluid which absorbs solar energy or, according to the case, to empty said space of said second fluid and to substitute said first fluid for it.
Also preferably, the glazing according to the invention is such that the periphery of the glazing includes an expansion volume for absorbing expansions of the second fluid depending on the temperature. This expansion volume may notably be achieved by means of free volume inside the bead located at the upper portion of the glazing.
Advantageously, the thickness of the inter-wall space is larger than or equal to 1 millimeter and less than or equal to 2 millimeters. Such a thickness is sufficiently large so that water in the liquid state may act, with the properties of a back body, it is sufficiently small for blocking convective motions.
The glazing according the present invention may be applied to the thermal preconditioning of the passenger compartment of a vehicle, to the creation of a window in dwelling premises, to the creation of greenhouses.